1. Exploratory Data Analysis
1.2. EDA Assumptions
1.2.5. Consequences

1.2.5.3.

Consequences of Non-Fixed Variation Parameter

Variation Estimate

The usual estimate of variation is the standard deviation

$$s_Y = \frac{1}{\sqrt{(N-1)}} \sqrt{\sum_{i=1}^{N} {(Y_i - \bar{Y})^2}}$$

from N measurements Y₁, Y₂, ... , Y_N.

Consequences of Non-Fixed Variation

If the run sequence plot does not support the assumption of fixed variation, then

1. The variation may be drifting.

2. The single variation estimate may be meaningless (if the process variation is drifting).

3. The variation estimate may be poor.

4. The variation estimate may be biased.